1. Field of the Invention
The present invention relates to a solid fuel furnace having an insulated firebox providing a two stage heating process wherein solid fuel is burned in a first chamber and volatile gases released by the fuel are burned in a second chamber.
2. State of the Prior Art
Furnaces and stoves in which solid fuel such as wood blocks and the like are burned have enjoyed great success. Such stoves have often included an insulated chamber in which fuel is placed and a means for providing combustion air to the chamber. Typically, this combustion air is brought underneath a grate on which the fuel is laid, with the air drawn into the stove through a forced air system. It is also known that if a high temperature can be maintained within a furnace, volatile gases released by the fuel during burning may be combusted to thereby add to the efficiency of the heating process.
One such stove which burns volatile gases released by the burning fuel is disclosed in the Canney U.S. Pat. No. 4,111,181, issued Sept. 5, 1978. The U.S. Pat. No. 4,111,181 discloses a wood burning stove including a grate on which fuel is placed wherein primary combustion air is introduced from beneath the grate. A smoke shelf or baffle is provided within the stove to direct gases released by the burning fuel to a secondary chamber through a plurality of tubes. In this secondary chamber, additional air is provided for burning of the gases. In this way, a more efficient stove is provided since the volatile gases are burned before being released to the atmosphere.
The Zimmer U.S. Pat. No. 4,157,704, issued June 12, 1979, shows a fireplace stove including a conventional grate on which wood is burned wherein combustion air is brought up from beneath the grate. The bottom portion of the stove may be provided with a firebrick lining in order to provide a structure resistant to high temperatures. Similar to this is the stove shown in the McIntire et al U.S. Pat. No. 4,117,824, issued Oct. 3, 1978, including a bottom portion provided with a plurality of firebricking which form a trough-like structure for supporting fuel thereon.
The Cagle U.S. Pat. No. 4,149,671, issued Apr. 17, 1979, discloses a solid fuel furnace including a forced air supply for providing combustion air underneath a grate which supports wood blocks or the like. The furnace shown in U.S. Pat. No. 4,149,671 provides heat by passing an air supply in a heat exchange relationship through baffles disposed about the fuel burning area. The Baker U.S. Pat. No. 4,127,100, issued on Nov. 28, 1978, discloses a wood burning stove which may be lined with firebrick to provide resistance to high temperatures generated by burning of the fuel. The heat given off by the fuel is passed in a heat exchange relationship with a pipe carrying ambient air to thereby heat the air and provide a source of heat in addition to that radiated by the stove.
The Morton et al U.S. Pat. No. 3,168,088, issued Feb. 2, 1965, discloses a stove including a grate for supporting logs or the like thereon, wherein the combustion chamber includes a damper device for controlling air flow to the fuel. The damper operates in response to the temperature inside the combustion chamber.
As can be seen from the foregoing, solid fuel burning stoves which attempt to increase the efficiency of the heating process by burning combustion gases released by the fuel have been used in the past. One problem with such stoves is that the temperature generated within the combustion chamber was often not sufficient to burn these gases. Additionally, the use of grates to support the fuel required a supply of combustion air provided beneath the grate. This type of air intake would often cool gases already present in the chamber and force the hot gases to the top of the stove and thereby reduce any burning thereof. Other methods of burning such volatile gases released by the fuel necessitated a complex recirculation pipe and forced air drafts in order to provide sufficient heat and air to burn the volatile gases.